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<tt>SWIG/Examples/tcl/class/</tt>
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<H2>Wrapping a simple C++ class</H2>

<p>
This example illustrates the most primitive form of C++ class wrapping performed
by SWIG.  In this case, C++ classes are simply transformed into a collection of
C-style functions that provide access to class members.

<h2>The C++ Code</h2>

Suppose you have some C++ classes described by the following (and admittedly lame) 
header file:

<blockquote>
<pre>
/* File : example.h */

class Shape {
public:
  Shape() {
    nshapes++;
  }
  virtual ~Shape() {
    nshapes--;
  }
  double  x, y;
  void    move(double dx, double dy);
  virtual double area() = 0;
  virtual double perimeter() = 0;
  static  int nshapes;
};

class Circle : public Shape {
private:
  double radius;
public:
  Circle(double r) : radius(r) { }
  virtual double area();
  virtual double perimeter();
};

class Square : public Shape {
private:
  double width;
public:
  Square(double w) : width(w) { }
  virtual double area();
  virtual double perimeter();
};
</pre>
</blockquote>

<h2>The SWIG interface</h2>

A simple SWIG interface for this can be built by simply grabbing the header file
like this:

<blockquote>
<pre>
/* File : example.i */
%module example

%{
#include "example.h"
%}

/* Let's just grab the original header file here */
%include "example.h"
</pre>
</blockquote>

Note: when creating a C++ extension, you must run SWIG with the <tt>-c++</tt> option like this:
<blockquote>
<pre>
% swig -c++ -tcl example.i
</pre>
</blockquote>

<h2>Some sample Tcl scripts</h2>

SWIG performs two forms of C++ wrapping-- a low level interface and a high level widget-like interface.
<ul>
<li>
Click <a href="runme.tcl">here</a> to see a script that calls the C++ functions using the
low-level interface.
<li>
Click <a href="runme2.tcl">here</a> to see the same script written with the high-level
interface.
</ul>

<h2>Key points</h2>

<ul>
<li>The low-level C++ interface works like this:
<p>
<ul>
<li>To create a new object, you call a constructor like this:

<blockquote>
<pre>
set c [new_Circle 10.0]
</pre>
</blockquote>

<p>
<li>To access member data, a pair of accessor functions are used.
For example:

<blockquote>
<pre>
Shape_x_set $c 15        ;# Set member data
set x [Shape_x_get $c]   ;# Get member data
</pre>
</blockquote>

Note: when accessing member data, the name of the base class must
be used such as <tt>Shape_x_get</tt>

<p>
<li>To invoke a member function, you simply do this

<blockquote>
<pre>
puts "The area is [Shape_area $c]"
</pre>
</blockquote>

<p>
<li>Type checking knows about the inheritance structure of C++. For example:

<blockquote>
<pre>
Shape_area $c       # Works (c is a Shape)
Circle_area $c      # Works (c is a Circle)
Square_area $c      # Fails (c is definitely not a Square)
</pre>
</blockquote>

<p>
<li>To invoke a destructor, simply do this

<blockquote>
<pre>
delete_Shape $c     # Deletes a shape
</pre>
</blockquote>

<p>
<li>Static member variables are wrapped as C global variables.  For example:

<blockquote>
<pre>
set n $Shape_nshapes    # Get a static data member
set Shapes_nshapes 13   # Set a static data member
</pre>
</blockquote>

</ul>

<p>
<li>The high-level interface works like a Tk widget

<p>
<ul>
<li>To create a new object, you call a constructor like this:

<blockquote>
<pre>
Circle c 10      # c becomes a name for the Circle object
</pre>
</blockquote>

<p>
<li>To access member data, use cget and configure methods.
For example:

<blockquote>
<pre>
c configure -x 15        ;# Set member data
set x [c cget -x]        ;# Get member data
</pre>
</blockquote>

<p>
<li>To invoke a member function, you simply do this

<blockquote>
<pre>
puts "The area is [c area]"
</pre>
</blockquote>

<p>
<li>To invoke a destructor, simply destroy the object name like this:

<blockquote>
<pre>
rename c ""         # c goes away
</pre>
</blockquote>

<p>
<li>Static member variables are wrapped as C global variables.  For example:

<blockquote>
<pre>
set n $Shape_nshapes    # Get a static data member
set Shapes_nshapes 13   # Set a static data member
</pre>
</blockquote>

</ul>
</ul>

<h2>General Comments</h2>

<ul>

<li>The low-level function interface is much faster than the high-level interface.
In fact, all the higher level interface does is call functions in the low-level interface.

<li>SWIG <b>does</b> know how to properly perform upcasting of objects in an inheritance
hierarchy (including multiple inheritance).  Therefore it is perfectly safe to pass
an object of a derived class to any function involving a base class.

<li>C++ Namespaces - %nspace isn't yet supported for Tcl.

</ul>

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